Trajectory Optimization And Communication Resource Allocation For UAV Alternate Relay Communication Systems

The development of contemporary mobile communication networks has entered the fifth generation.With the gradual expansion of the scope of human activities,the demand for communication has increased dramatically,and higher requirements have been put forward for the development of wireless communication technology.Unmanned Aerial Vehicle(UAV)relays have outstanding advantages such as high flexibility,low cost,and survivability,and can well make up for the defects of traditional relays such as poor maneuverability,fragility,and high cost.However,the existing research and applications of UAV relays often face problems such as low spectrum utilization and limited coverage.In order to solve these problems,this thesis considers a dual-UAV alternate relay communication system model and conducts in-depth research from the perspectives of transmit power,flight trajectory,and user communication scheduling.It mainly includes the following two parts:(1)The trajectory design and power allocation in alternate relay communication system are studied.The system consists of one source,two UAV relays and one destination.Two UAV relays work alternately to transmit information from a source to a destination.To improve the spectrum utilization of the UAV relay communication system and coordinate the interference between two relaying links,the throughput of the whole alternate relay communication system is maximized by jointly optimizing the flight trajectory of UAV relay and the transmission power of the source and UAV relays.The involved optimization problems are constrained by mobility and collision avoidance constraints of the UAVs,and the peak power and average power constraints of each transmitter,which is non-convex and difficult to obtain the optimal solution.In this thesis,we propose an effective iterative algorithm to solve this problem suboptimally by using the alternating optimization and successive convex optimization methods.Simulation results have verified the effectiveness of the proposed algorithm.(2)With the increasing number of cell-edge users,new requirements for communication coverage are put forward.Based on our previous work,we further study the multi-user communication scheduling and relay trajectory optimization in the alternate relay communication system.The system is composed of a single source,two UAV relays and multiple destination users,which can be better applied to long-distance multi-user communication.To improve the spectral efficiency and coordinate interference among the relaying data links,the system throughput is maximized by optimizing the downlink user communication scheduling and UAV relay trajectory.The resultant optimization problem is subject to the mobility and collision avoidance of the UAV relays,which is a non-convex optimization problem that is difficult to solve.An effective iterative algorithm based on the continuous convex optimization technique is proposed to alternately optimize user scheduling and UAV relays’ flight trajectories.Simulation results show the superiority of the proposed algorithm.